Characterizing ablation lesions using optical coherence tomography (OCT)

ABSTRACT

Systems, methods, and other embodiments associated with characterizing Radio Frequency Ablation (RFA) lesions using Optical Coherence Tomography (OCT) are described. One example method includes acquiring an OCT signal from a Region Of Interest (ROI) in an ablated material. The example method may also include determining whether a lesion was formed by the ablation by analyzing optical properties of the ROI as recorded in the OCT signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication 61/230,281 filed Jul. 31, 2009.

FEDERAL FUNDING NOTICE

The invention was developed with federal funding supplied under FederalGrant No. 1R01HL08304 and 1F31HL085939 provided by NIH. The Federalgovernment has certain rights in the invention.

BACKGROUND

2.5 million people in the U.S. have cardiac arrhythmias that cannot becontrolled with traditional treatments. Ablation is one treatment forcardiac arrhythmias. Ablation destroys tissue that triggers or supportsabnormal electrical pathways in tissue. Cardiac ablation attempts totarget and eradicate the tissue of the abnormal electrical pathway,while avoiding normal tissue. Conventional ablation techniques uselow-resolution images acquired by fluoroscopy or static images fromcomputed tomography merged onto fluoroscopy. These techniques monitorthe ablation by measuring tissue temperature, impedance at the surfaceof the tissue, and other indirect methods. Indirect methods ofmonitoring the ablation may result in delivering more lesions thannecessary and prolonging procedure times. Traditionally, directlyvisualizing critical intra-cardiac structures in the heart whenperforming ablation was not feasible.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate various example systems, methods,and other example embodiments of various aspects of the invention. Itwill be appreciated that the illustrated element boundaries (e.g.,boxes, groups of boxes, or other shapes) in the figures represent oneexample of the boundaries. One of ordinary skill in the art willappreciate that in some examples one element may be designed as multipleelements or that multiple elements may be designed as one element. Insome examples, an element shown as an internal component of anotherelement may be implemented as an external component and vice versa.Furthermore, elements may not be drawn to scale.

FIG. 1 illustrates an example method associated with determining whethera lesion is present in a material.

FIG. 2 illustrates an example device associated with determining whethera lesion is present in a material.

FIG. 3 illustrates an example computing environment in which examplesystems, apparatus, methods, and equivalents, may operate.

FIG. 4 illustrates an example method associated with real-time OCTimaging of a material.

FIG. 5 illustrates an example method associated with using real-time OCTto determine a lesion's development stage.

FIG. 6 illustrates another example method associated with usingreal-time OCT to determine a lesion's development stage and determiningwhen to end ablation based on the real-time OCT image.

FIG. 7 illustrates an example OCT device for use in a catheterassociated with ablating a material and acquiring real-time OCT signalsof the material being ablated.

FIG. 8 illustrates an example rotary joint mechanism for rotating an OCTdevice lens.

FIG. 9 illustrates an example catheter for acquiring real-time OCTsignals and ablating a Region of Interest.

FIG. 10 illustrates another example of a catheter for acquiring OCTsignals.

FIG. 11 illustrates an example catheter for acquiring OCT signals.

FIG. 12 illustrates an example optical assembly in a catheter foracquiring OCT signals.

FIG. 13 illustrates one specific example of an optical assembly in acatheter for acquiring OCT signals.

FIG. 14 illustrates an example in vivo experiment for acquiring OCTsignals.

FIG. 15 illustrates an example in vivo experiment for acquiring OCTsignals.

DETAILED DESCRIPTION

Systems, apparatus, and methods associated with determining whether alesion is present in a material are described.

References to “one embodiment”, “an embodiment”, “one example”, “anexample”, indicate that the embodiment(s) or example(s) so described mayinclude a particular feature, structure, characteristic, property,element, or limitation, but that not every embodiment or examplenecessarily includes that particular feature, structure, characteristic,property, element or limitation. Furthermore, repeated use of the phrase“in one embodiment” does not necessarily refer to the same embodiment,though it may.

Some portions of the detailed descriptions that follow are presented interms of algorithms and symbolic representations of operations on databits within a memory. These algorithmic descriptions and representationsare used by those skilled in the art to convey the substance of theirwork to others. An algorithm, here and generally, is conceived to be asequence of operations that produce a result. The operations may includephysical manipulations of physical quantities. Usually, though notnecessarily, the physical quantities take the form of electrical ormagnetic signals capable of being stored, transferred, combined,compared, and otherwise manipulated in a logic. The physicalmanipulations create a concrete, tangible, useful, real-world result.

It has proven convenient at times, principally for reasons of commonusage, to refer to these signals as bits, values, elements, symbols,characters, terms, and numbers. It should be borne in mind, however,that these and similar terms are to be associated with the appropriatephysical quantities and are merely convenient labels applied to thesequantities. Unless specifically stated otherwise, it is appreciated thatthroughout the description, terms including processing, computing, anddetermining, refer to actions and processes of a computer system, logic,processor, or similar electronic device that manipulates and transformsdata represented as physical (electronic) quantities.

Example methods may be better appreciated with reference to flowdiagrams. While for purposes of simplicity of explanation, theillustrated methodologies are shown and described as a series of blocks,it is to be appreciated that the methodologies are not limited by theorder of the blocks, as some blocks can occur in different orders and/orconcurrently with other blocks from that shown and described. Moreover,less than all the illustrated blocks may be required to implement anexample methodology. Blocks may be combined or separated into multiplecomponents. Furthermore, additional and/or alternative methodologies canemploy additional, not illustrated blocks.

FIG. 1 illustrates a method 100 associated with determining whether alesion is present in a material. Method 100 may include, at 110,acquiring an Optical Coherence Tomography (OCT) signal from a Region ofInterest (ROI) in a material subjected to ablation. The ablation may be,for example, Radio Frequency Ablation (RFA), High Intensity FocusedUltrasound (HIFU) ablation, laser ablation, or cryoablation. Thematerial may be tissue, for example, myocardial tissue, skeletal muscletissue, intestinal tissue, and so on. In tissue, ablation may causenecrosis of the tissue at the ablation point. This necrosis may create alesion that has different optical properties than normal non-ablatedtissue.

For example, myocardium is covered by a thin layer, called theepicardium, which appears highly reflective within OCT images. Normalmyocardium has a characteristic birefringence artifact, due to thehighly organized structure of fibers in the myocardium. Epicardial fathas a heterogeneous appearance within OCT images. Adipose tissue iscovered by a layer of epicardial cells and connective tissue thatappears as a bright layer within OCT images. Coronary vessels appear assignal poor regions, corresponding to the empty vessel lumens embeddedin a layer superficial to the myocardium. The location of the vessellumens correspond with the location of the vessels apparent inmicroscope images.

The distinct features of the epicardium, myocardium, epicardial fat andcoronaries are visible within slices parallel to the epicardial surface,and correlate to the microscope images of the surface. Within theimages, a thick epicardial layer is observed which covers epicardialfat, which in turn surrounds the coronary vessel. Untreated myocardiumis characterized by a polarization artifact and an epicardial layer anda coronary vessel images encompassing epicardial fat, which appearsheterogeneous. Therefore, viable tissue is characterized by apolarization artifact dark band within conventional OCT images due tothe birefringence property of the highly organized myocardial tissue.

However, ablated myocardial tissue has different optical properties.Specifically, with the application of RF energy and lesion formation,the contrast between the epicardium and myocardium and the polarizationdependent artifact is lost. Moreover, an ablated region of myocardialtissue impedes the conducting of an electrical signal through part ofthe tissue. Ablating a region of myocardial tissue that abnormallyconducts an electrical signal is therefore useful in treatingarrhythmias. Thus, method 100 may be used to treat myocardialarrhythmias in an intra-cardiac RFA procedure.

Method 100 may also include, at 120, controlling an apparatus todetermine whether a lesion was formed by the ablation. Determiningwhether a lesion was formed is performed by analyzing optical propertiesof the ROI as recorded in the OCT signal. The difference in opticalproperties between viable non-ablated tissue and ablated tissue isuseful in determining whether ablation of a region of tissue wassuccessful in forming a lesion. The optical properties of the ROI thatmay be analyzed may include, for example, birefringence, anisotropy,absorption, light attenuation rate, backscattering, tissue scattering,mean intensity, and tissue heterogeneity.

The optical properties of the ROI as recorded in the OCT signal alsofacilitate determining tissue architecture. Tissue architecture mayinclude, for example, fiber orientation, epicardial fat and structuresincluding coronary vessels, atrio-ventricular nodes, and sino-atrialnodes.

Determining whether the lesion was formed includes applyingsignal-processing techniques to the OCT signal. For example, the OCTsignal may be processed by applying a single scattering model, or aLaplacian of Gaussian (LoG) to the OCT signal. Applyingsignal-processing techniques to the OCT signal provides values for theoptical properties. These values facilitate determining whether a lesionexists in the material from the ablation. Determining whether a lesionexists may also include determining a lesion size, and a lesion depthfrom the optical properties.

Indications of a lesion may include, for example, a decrease inbirefringence, an increased signal intensity, a decreased signalattenuation rate, a decreased gradient strength, an increasedheterogeneity, an increased scattering, and an increased imaging depth.Birefringence may be detected by filtering with a LoG to quantifygradient strength with a conventional OCT system; signal differences inthe two channels of a polarization diverse detection OCT system; andretardance measurements using a polarization sensitive OCT system. Anattenuation coefficient may facilitate calculating a lesion depth. Theattenuation coefficient may indicate tissue scattering. In one example,the attenuation coefficient increases with an increasing lesion depth. Abackscattering coefficient may indicate reflectivity. A correlationcoefficient can quantify how well an OCT signal fits a mathematicalmodel of light-tissue interaction. The correlation coefficient mayindicate heterogeneity.

A Region of Interest (ROI) may be, for example, a portion of materialthat is being ablated, a portion of material that was ablated, or aportion of material that may be ablated. Acquiring an OCT signal from aROI prior to ablating the ROI facilitates controlling an apparatus todetermine whether to target the ROI for ablation, or to avoid ablatingthe ROI. Ablation of a ROI that includes, for example, coronary vesselsmay be avoided by acquiring and processing an OCT signal from the ROIprior to ablation.

Acquiring the OCT signal may include using Polarization Sensitive OCT(PS-OCT), a polarization diverse detection OCT system, a conventionalOCT, or Fourier Domain OCT (FDOCT). Example FDOCT systems includespectral domain FDOCT systems (SDOCT) and swept source FDOCT systems(SSOCT). The optical properties of the ROI recorded in the OCT signalmay also include retardation, and a spectral interference pattern.

While FIG. 1 illustrates various actions occurring in serial, it is tobe appreciated that various actions illustrated in FIG. 1 could occursubstantially in parallel. By way of illustration, a first process couldacquire the OCT signal, and a second process could determine whether alesion is present. While two processes are described, it is to beappreciated that a greater and/or lesser number of processes could beemployed and that lightweight processes, regular processes, threads, andother approaches could be employed.

In one example, a method may be implemented as computer executableinstructions. Thus, in one example, a computer-readable medium may storecomputer executable instructions that if executed by a machine (e.g.,processor) cause the machine to perform a method that includesdetermining whether a lesion was generated by an ablation in the ROI asa function of optical properties of the ROI as registered in the OCTsignal. While executable instructions associated with the above methodare described as being stored on a computer-readable medium, it is to beappreciated that executable instructions associated with other examplemethods described herein may also be stored on a computer-readablemedium.

A “computer readable medium”, as used herein, refers to a medium thatstores signals, instructions and/or data. A computer readable medium maytake forms, including, but not limited to, non-volatile media, andvolatile media. Non-volatile media may include, for example, opticaldisks, and magnetic disks. Volatile media may include, for example,semiconductor memories, and dynamic memory. Common forms of a computerreadable medium may include, but are not limited to, a floppy disk, aflexible disk, a hard disk, a magnetic tape, other magnetic medium, anapplication specific integrated circuit (ASIC), a compact disk CD, otheroptical medium, a random access memory (RAM), a read only memory (ROM),a memory chip or card, a memory stick, and other media from which acomputer, a processor or other electronic device can read.

FIG. 2 illustrates an example device 200 associated with controlling anapparatus to determine whether a lesion was generated by an ablation ina ROI. Device 200 may include a detector 210 to acquire an OCT signal230 from a ROI in a material. Device 200 may also include a developmentlogic 220 configured to control an apparatus to determine whether alesion was generated by an ablation in the ROI based, at least in part,on optical properties of the ROI as registered in the OCT signal 230.The ablation may be, for example, RFA, HIFU ablation, laser ablation,cryoablation, and so on. The material may be myocardial tissue, a tissuethat exhibits anisotropic optical properties, and so on.

The development logic 220 determines whether the lesion was generated byapplying signal-processing techniques to the OCT signal 230. Processingthe OCT signal 230 may result, for example, in determining discretevalues for the optical properties of the OCT signal. The opticalproperties of the ROI that may be provided from this processing are, forexample, birefringence, anisotropy, absorption, light attenuation rate,backscattering, tissue scattering, mean intensity, and tissueheterogeneity. These discrete values facilitate determining whether alesion exists in the material from the ablation. The processingtechniques that may be used include a single scattering model, or aLaplacian of Gaussian (LoG). The development logic 220 may alsodetermine a lesion size, and a lesion depth from the OCT signal 230.

The detector 210 acquires the OCT signal 230. In one embodiment thedevice 200 may be, for example, a conventional OCT, an OCT withpolarization diversity detection, a PS-OCT, or a FDOCT. The OCT may usea superluminescent diode (SLD) centered at 1310 nm with a 70 nm (FWHM)bandwidth as a light source.

Alternatively, the OCT may use a system having a light source centeredat 1310 nm with 70 nm bandwidth and a microscope integrated spectraldomain OCT. Spectral interferograms may be acquired with a linearin-wavenumber (k=2π/λ) spectrometer onto a 1024 pixel line scan cameraspectrometer, acquired at a 40 kHz line scan rate. An example system mayhave a 4.3 mm imaging range, 2 mm-6 dB fall off range, and 110 dBsensitivity. The axial and lateral resolution of the system is 16 and 12micrometers (in air) respectively. Images may be 4 mm in transverselength, 1000 lines per image, and 512 pixels per line. A volume mayconsist of 400 images. An index of refraction of 1.38 for ventriculartissue, with the dimensions of the volume being 4 mm×4 mm×3.11 mm (L, W,H), has a corresponding pixel resolution of 4 μm, 10 μm, and 6 μmrespectively. Summed voxel projection may be used for rapidvisualization of the three dimensional image sets and planes parallel tothe sample surface are obtained by detecting the surface with anintensity threshold and digitally flattening the tissue surface.

Detector 210 may also be a detector associated with a conventional OCT,a PS-OCT, or a FDOCT as understood by one of ordinary skill in the art.A low coherence interferometer or a polarimeter may also be used toacquire and analyze signals from a ROI.

FIG. 3 illustrates an example computing device in which example systemsand methods described herein, and equivalents, may operate. The examplecomputing device may be a computer 300 that includes a processor 302, amemory 304, and input/output ports 310 operably connected by a bus 308.In one example, the computer 300 may include an OCT logic 330 configuredto control an apparatus to determine whether a lesion was generated byan ablation in the ROI based, at least in part, on optical properties ofthe ROI as registered in the OCT signal. In different examples, thelogic 330 may be implemented in hardware, firmware, and/or combinationsthereof. While the logic 330 is illustrated as a hardware componentattached to the bus 308, it is to be appreciated that in one example,the logic 330 could be implemented in the processor 302.

Logic 330 may provide means (e.g., hardware, firmware) for acquiring anOCT signal from a ROI in a material. The means may be implemented, forexample, as an ASIC programmed to acquire an OCT signal. The means mayalso be implemented as computer executable instructions that arepresented to computer 300 as data 316 that are temporarily stored inmemory 304 and then executed by processor 302. Logic 330 may alsoprovide means (e.g., hardware, firmware) for controlling an apparatus todetermine whether a lesion exists in the ROI from an ablation as afunction of optical properties of the ROI as recorded in the OCT signal.

Generally describing an example configuration of the computer 300, theprocessor 302 may be a variety of various processors including dualmicroprocessor and other multi-processor architectures. A memory 304 mayinclude volatile memory and/or non-volatile memory. Non-volatile memorymay include, for example, Read Only Memory (ROM), and Programmable ROM(PROM). Volatile memory may include, for example, Random-Access Memory(RAM), Static RAM (SRAM), and Dynamic RAM (DRAM).

A disk 306 may be operably connected to the computer 300 via, forexample, an input/output interface (e.g., card, device) 318 and aninput/output port 310. The disk 306 may be, for example, a magnetic diskdrive, a solid-state disk drive, a floppy disk drive, a tape drive, aZip drive, a flash memory card, and a memory stick. Furthermore, thedisk 306 may be a Compact Disc ROM (CD-ROM) drive, a CD Recordable(CD-R) drive, a CD ReWritable (CD-RW) drive, and a Digital VersatileDisc ROM (DVD ROM). The memory 304 can store a process 314 and/or a data316, for example. The disk 306 and/or the memory 304 can store anoperating system that controls and allocates resources of the computer300.

The bus 308 may be a single internal bus interconnect architectureand/or other bus or mesh architectures. While a single bus isillustrated, it is to be appreciated that the computer 300 maycommunicate with various devices, logics, and peripherals using otherbusses (e.g., Peripheral Component Interconnect Express (PCIE), 1394,Universal Serial Bus (USB), Ethernet). The bus 308 can be typesincluding, for example, a memory bus, a memory controller, a peripheralbus, an external bus, a crossbar switch, and/or a local bus.

The computer 300 may interact with input/output devices via the i/ointerfaces 318 and the input/output ports 310. Input/output devices maybe, for example, a keyboard, a microphone, a pointing and selectiondevice, cameras, video cards, displays, the disk 306, and the networkdevices 320. The input/output ports 310 may include, for example, serialports, parallel ports, and USB ports.

The computer 300 can operate in a network environment and thus may beconnected to the network devices 320 via the i/o interfaces 318, and/orthe i/o ports 310. Through the network devices 320, the computer 300 mayinteract with a network. Through the network, the computer 300 may belogically connected to remote computers. Networks with which thecomputer 300 may interact include, but are not limited to, a Local AreaNetwork (LAN), a Wide Area Network (WAN), and other networks.

FIG. 4 illustrates an example method 400 associated with real-time OCTimaging of a material. At 410, method 400 acquires an OCT signal from aROI in a material while ablating the ROI. The material may be tissue,including myocardial tissue. At 420, method 400 controls an apparatus tostop ablating the ROI. Determining whether to stop the ablating may bebased on receiving an input signal, determining whether a lesion hasformed from the ablating, or when an onset of complications is detected.Determining whether a lesion has formed is a function of analyzingoptical properties of the ROI as recorded in the OCT signal. The opticalproperties of the ROI may be, for example, birefringence, anisotropy,absorption, light attenuation rate, backscattering, tissue scattering,mean intensity, and tissue heterogeneity. In one embodiment, method 400may continuously acquire and process OCT signals from the ROI duringablation. In another embodiment, method 400 may intermittently acquireand process OCT signals from the ROI during ablation. This real-timeacquiring and processing of OCT signals facilitates forming lesions inthe treatment of arrhythmia in myocardial tissue by ablation.

FIG. 5 illustrates an example method 500 associated with determining alesion's development stage using real-time OCT. At 510, method 500acquires an OCT signal from a ROI in a material while ablating the ROI.Method 500 controls an apparatus, at 520, to determine a lesion'sdevelopment stage in the ROI as a function of optical properties of theROI as recorded in the OCT signal. Ablating the ROI to form a lesion maybe viewed as a gradual process. The lesion progresses through differentdevelopment stages while ablating the ROI. For example, the lesionbegins as a small disturbance while initially ablating the ROI.Continuing to ablate the ROI causes the lesion to progress. After avariable amount of time, the lesion will reach a desirablecharacteristic. The lesion may progress to an undesirable developmentstage if ablating is allowed to continue beyond an appropriate time.Lesion development progression in an ROI can be correlated with changesin optical properties and electrical properties of the ROI.

FIG. 6 illustrates another example method 600 associated with stoppingthe ablation of a ROI based on a lesion's development stage. Similar tomethod 500, method 600 acquires an OCT signal from an ROI in a materialduring ablation, at 610. At 620, method 600 controls an apparatus todetermine a lesion's development stage in the ROI. The lesion'sdevelopment stage may be determined based on, for example, opticalproperties of the ROI as recorded in the OCT signal. The opticalproperties of the ROI are, for example, birefringence, anisotropy,absorption, light attenuation rate, backscattering, tissue scattering,and tissue heterogeneity.

Determining the lesion's development stage from optical properties ofthe ROI may include calculating, for example, a decrease inbirefringence, an increased signal intensity, a decreased signalattenuation rate, a decreased gradient strength, an increasedheterogeneity, an increased scattering, and an increased imaging depth.An attenuation coefficient may facilitate calculating a lesion depth.The attenuation coefficient may indicate tissue scattering. In oneexample, the attenuation coefficient increases with an increasing lesiondepth. A backscattering coefficient may indicate reflectivity. Acorrelation coefficient can quantify how well an OCT signal fits amathematical model of light-tissue interaction. The correlationcoefficient may indicate heterogeneity. The amount of change in theoptical properties indicates the lesion's development stage. The opticalproperties gradually change as the lesion progresses during ablation.For example, birefringence may be detected by filtering with a LoG toquantify gradient strength with a conventional OCT system; signaldifferences in the two channels of a polarization diverse detection OCTsystem; and retardance measurements using a polarization sensitive OCTsystem. A gradual decrease of birefringence as ablation continuesindicates a lesion progressing through development stages. Determining alesion's development stage may also include determining a lesion size,and a lesion depth.

At 630, method 600 controls the apparatus to stop ablating the ROI whenit is determined that the lesion is a clinically relevant lesion, or aborderline overtreatment lesion. Overtreatment may be characterized, forexample, by disruptions in the myocardium and increased tissueheterogeneity. A clinically relevant lesion is, for example, a lesionthat changes the electrical properties of the ROI to impede conductingan electrical signal across the ROI. Ideally, a clinically relevantlesion does not exhibit signs of overtreatment. Overtreatment of an ROImay include, for example, steam pops, or craters in the ROI. Determiningthe lesion is a borderline overtreatment lesion may include determiningan attenuation coefficient and a correlation coefficient for the OCTsignal.

Implementing the methods, systems, and devices discussed above mayreduce procedure times for treating cardiac arrhythmias, in some casesover eighty percent. In one example, the procedure time using thesemethods, systems, and devices is less than three hours.

FIG. 7 illustrates an example OCT device optical assembly 700 for use ina catheter associated with ablating a material and acquiring real-timeOCT signals of the ablating. The assembly 700 may include, for example,a torsion cable 710. The torsion cable 710 facilitates rotating aGradient-Index (GRIN) lens 720. In one embodiment, the GRIN lens 720 maybe configured to couple to an optical fiber 750. The optical fiber 750facilitates acquiring OCT signals from a material. The optical window730 provides protection for the components of OCT device 700 fromforeign matter. A sheath 740 provides structure and, similar to theoptical window 730, also provides protection from foreign matter. Insome embodiments, the assembly 700 is made from Magnetic ResonanceImaging (MRI) and RF energy compatible materials.

FIG. 8 illustrates an example rotary joint mechanism 800 for rotating anOCT device optical assembly 805. The rotary joint mechanism 800 mayinclude, for example, rotary joint 820 for allowing the OCT deviceoptical assembly 805 to rotate. The rotary joint 820 is configured tocause a torsion cable 850 or an optical fiber 840 to rotate and applytorque to the OCT device optical assembly 805 causing the OCT deviceoptical assembly 805 to rotate. The rotary joint mechanism 800 may alsoinclude a static sheath holder 810. The static sheath holder 810prevents a sheath 860 in the OCT device from rotating. The rotarymechanism 800 may also include a static fiber holder 830 to prevent anoptical fiber 840 from rotating.

FIG. 9 illustrates an example catheter for acquiring real-time OCTsignals and ablating a Region of Interest. The catheter 900 may includean OCT device optical assembly 910 similar to the OCT device opticalassembly 700. The catheter 900 is configured to deliver Radio Frequency(RF) energy 930 suitable to ablate a Region of Interest (ROI) from aRadio Frequency Ablation (RFA) device. The catheter 900 is made fromMagnetic Resonance Imaging (MRI) and RF energy compatible materials. Thecatheter 900 facilitates OCT imaging while ablating a ROI with RF energy930. In some embodiments, the catheter 900 may be miniaturized andintegrated into RF or other ablation catheters.

FIG. 10 illustrates another example catheter 1000 for acquiring OCTsignals. The catheter 1000 includes sheath 1010. The composition ofsheath 1010 may include, for example, polytetrafluoroethylene (PTFE),ceramic, polyetheretherketone (PEEK), an RF compatible material, and soon. An RF compatible material is a material that resists heating when RFenergy is applied to the material. The catheter 1000 also includes afiber optic cable 1020. The fiber optic cable 1020 may be, for example,SMF-28e cable with a tight buffer PVC, and so on. Ring jewel bearings1030 and 1080 may be, for example, sapphire. The end cap 1040 protectsthe optical assembly from contamination. The catheter 1000 may include aferrule 1050 that maintains the fiber optic cable 1020 in properalignment. The optical assembly of the catheter 1000 may include aGradient Index Lens (GRIN) 1060, a Risley prism 1070, and optical glass1090.

FIG. 11 illustrates an example catheter 1100 for acquiring OCT signals.The catheter 1100 may include, for example, a sheath 1110, a ring jewelbearing 1120, a ring jewel bearing 1125, a split sleeve 1130, a GRINlens 1140, a Risley prism 1145, a sheath tip 1150, a window 1160, aferrule 1170, and a fiber optic cable 1180 with a tight buffer 1185. Thesheath 1110 may be composed of, for example, PTFE. The ring jewelbearings 1120 and 1125 may be composed of, for example, sapphire. Thesplit sleeve 1130 may be, for example, ceramic. The sheath tip 1150 maybe, for example, PEEK. The window 1160 may be, for example, fusedsilica. The ferrule 1170 may be, for example, glass or ceramic. Thefiber optic cable 1180 may be, for example, a SMF-28e cable. The tightbuffer 1185 may be, for example, PVC.

Catheter 1100 facilitates imaging a ROI with OCT using forward lookingimaging. Forward looking imaging is imaging that occurs through the endof a catheter. To accomplish this, the fiber optic cable 1180 rotateswithin the sheath tip 1150 to perform a generally circular scan of theROI. The ring jewel bearings 1120 and 1125 facilitate rotating whentorque is applied to the fiber optic cable 1180. The ring jewel bearings1120 and 1125 provide a low friction joint for rotating. Thus, thesheath tip 1150 remains stationary relative to the fiber optic cable1180, GRIN lens 1140, Risley prism 1145, and ferrule 1170 when rotatingthe fiber optic cable 1180.

In one example, catheter 1100 has a rigid end length of 18 mm and anouter diameter of 2.5 mm. Catheter 1100 has a scan diameter of 2 mm,which results in a 6.28 mm lateral scanning range. Catheter 1100maintains a FWHM spot size of less than 30 μm over an entire 1 mmworking range. Images using forward looking imaging are acquired at 40kHz line scan rate, 2000 lines per image, and 512 pixels per line. Thiscorresponds to a 6 μm and 3.1 μm pixel size in the axial and lateraldimensions respectively. A correlation based method may be used tocorrect for non-uniform scanning rates, removing highly correlated axialscans.

FIG. 12 illustrates an optical assembly 1200 that can be used in acatheter for acquiring OCT signals. The optical assembly 1200 mayinclude a fiber optic cable 1210, a GRIN lens 1220, a Risley prism 1230,and an optical glass window 1240. The optical assembly 1200 facilitatesimaging a ROI 1260 with an optical signal 1250. Optical assembly 1200may be used to perform generally circular scanning of ROI 1260. Therotating fiber optic cable 1210 also rotates GRIN lens 1220, Risleyprism 1230, and to obtain the OCT signal 1250. Thus, the rotating fiberoptic cable 1210 allows the optical assembly 1200 to facilitate imagingROI 1260 in a generally circular pattern.

In one example, a flexible forward scanning OCT catheter may be designedfor in-contact, circular-scan imaging in ex vivo or in vivo experiments.Ex vivo experiments may be conducted for varying time periods. In oneexample, ex vivo imaging is conducted for 90 seconds: 15 seconds priorto the start of RF energy delivery; 60 seconds during energy delivery;and 15 seconds after the conclusion of RF energy delivery. Ablation ofmaterial (e.g. myocardial tissue) with the purpose of forming a lesionis effective where the catheter is perpendicular to the material andthere is adequate contact between the catheter and the material. In oneexample, ex vivo ablation lesions may be created with a temperaturecontrolled protocol (e.g. 80° C.) with a maximum delivered power of 50W.

In vivo experiments, as show in FIG. 14, may also be conducted. In oneexample, to evaluate whether OCT can identify dynamic tissue change dueto RF energy delivery in vivo, an RF ablation catheter may be inserteddirectly into a right porcine atrium, as shown in FIG. 14( a). The RFablation catheter may be advanced and navigated within the heart underfluoroscopic guidance, as shown in FIG. 14( b). In one example, imagesof the endocardial surface and sub endocardial tissue may be obtainedwhen the RF ablation catheter is in direct contact with the endocardialsurface, as shown in FIG. 14( c). Image penetration may be significantlyreduced due to blood absorption and scattering without direct contact,as shown in FIG. 14( d).

In one example, an in vivo experiment may be conducted with temperaturecontrolled RF energy being delivered for 60 seconds, with a targettemperature of 85° C., after 15 seconds of imaging with stable contactwith the endocardial surface. The formation and progressive increase insize of cavities within tissue may be observed in OCT images like thoseof FIG. 14( c) and FIG. 14( d). Alternatively, the effects of the RFenergy can be visualized at different time intervals as shown in FIG.15.

FIG. 13 illustrates one specific embodiment of an optical assembly 1300in a catheter for acquiring OCT signals. Optical assembly 1300 mayinclude, for example, a fiber optic cable, a GRIN lens, a Risley prism,and an optical window composed of, for example, fused silica.

While example systems, methods, and other embodiments have beenillustrated by describing examples, and while the examples have beendescribed in considerable detail, it is not the intention of theapplicants to restrict or in any way limit the scope of the appendedclaims to such detail. It is, of course, not possible to describe everyconceivable combination of components or methodologies for purposes ofdescribing the systems, methods, and apparatus described herein.Therefore, the invention is not limited to the specific details, therepresentative apparatus, and illustrative examples shown and described.Thus, this application is intended to embrace alterations,modifications, and variations that fall within the scope of the appendedclaims.

To the extent that the term “includes” or “including” is employed in thedetailed description or the claims, it is intended to be inclusive in amanner similar to the term “comprising” as that term is interpreted whenemployed as a transitional word in a claim.

To the extent that the term “or” is employed in the detailed descriptionor claims (e.g., A or B) it is intended to mean “A or B or both”. Whenthe applicants intend to indicate “only A or B but not both” then theterm “only A or B but not both” will be employed. Thus, use of the term“or” herein is the inclusive, and not the exclusive use. See, Bryan A.Garner, A Dictionary of Modern Legal Usage 624 (2d. Ed. 1995).

To the extent that the phrase “one or more of, A, B, and C” is employedherein, (e.g., a data store configured to store one or more of, A, B,and C) it is intended to convey the set of possibilities A, B, C, AB,AC, BC, and/or ABC (e.g., the data store may store only A, only B, onlyC, A&B, A&C, B&C, and/or A&B&C). It is not intended to require one of A,one of B, and one of C. When the applicants intend to indicate “at leastone of A, at least one of B, and at least one of C”, then the phrasing“at least one of A, at least one of B, and at least one of C” will beemployed.

What is claimed is:
 1. A method, comprising: ablating a region ofinterest (ROI) in a material using an ablation catheter; acquiring anOptical Coherence Tomography (OCT) signal from the ablated ROI in thematerial, wherein the OCT is acquired by an OCT device within theablation catheter; and during the ablating, controlling an apparatuscoupled to the OCT device to determine a development stage of a lesionformed in the ablated ROI by analyzing an optical property of the ROI asrecorded in the OCT signal.
 2. The method of claim 1, wherein theablating ablation catheter employs one of Radio Frequency Ablation(RFA), High Intensity Focused Ultrasound (HIFU) ablation, laserablation, and cryoablation.
 3. The method of claim 1, wherein thematerial is myocardial tissue.
 4. The method of claim 3, wherein thedevelopment stage of the lesion is one of viable myocardial tissuecharacterized by a polarization artifact and myocardial tissue with thelesion characterized by the polarization artifact being lost.
 5. Themethod of claim 1, wherein the determining the development stage of thelesion further comprises determining one or more of: a lesion size and alesion depth.
 6. The method of claim 1, wherein the material comprisestissue; and wherein the optical properties of the ROI are one or moreof: birefringence, anisotropy, absorption, light attenuation rate,backscattering, tissue scattering, mean intensity, and tissueheterogeneity.
 7. The method of claim 1, wherein the determining thedevelopment stage of the lesion further comprises processing the OCTsignal with one or more of: a single scattering model and a Laplacian ofGaussian (LoG).
 8. The method of claim 1, wherein the OCT devicecomprises one of: a Polarization Sensitive OCT (PS-OCT) device, aconventional OCT device, a polarization diverse detection OCT device,and a Fourier Domain OCT (FDOCT) device to acquire the OCT signal. 9.The method of claim 1, wherein the optical properties of the ROIrecorded in the OCT signal are one or more of: retardation and aspectral interference pattern.
 10. The method of claim 1, furthercomprising: targeting the ROI with a subsequent ablation or avoiding theROI with the subsequent ablation based on the development stage of thelesion.
 11. The method of claim 1, wherein the ablated ROI in thematerial impedes conducting an electrical signal through part of thematerial.
 12. The method of claim 1, wherein the material comprisestissue; and further comprising determining a tissue architecture of thematerial based on the optical properties of the ROI as recorded in theOCT signal.
 13. The method of claim 1, wherein the acquiring the OCTsignal and the controlling the apparatus to determine the developmentstage of the lesion formed by the ablation occurs during anintra-cardiac Radio Frequency Ablation (RFA) procedure.
 14. The methodof claim 13, wherein the material is myocardial tissue and the ablationcomprises an intra-cardiac RFA procedure to treat a myocardialarrhythmia.
 15. The method of claim 1, further comprising controllingthe apparatus to stop ablating the ROI upon determining that thedevelopment stage of the lesion is a clinically relevant lesion stage.16. The method of claim 1, further comprising controlling the apparatusto stop ablating the ROI upon determining that the development stage ofthe lesion is a borderline overtreatment lesion stage.
 17. The method ofclaim 16, wherein the determining that the development stage of thelesion is a borderline overtreatment lesion stage further comprisesdetermining an attenuation coefficient and a correlation coefficient.18. The method of claim 1, wherein the analyzing the optical propertiesof the ROI as recorded in the OCT signal further comprises applying oneor more signal processing techniques to the OCT signal.
 19. The methodof claim 1, wherein the OCT device comprises an optical assembly coupledto an optical fiber and the ablation catheter comprises a radiofrequency ablation device that delivers radio frequency energy suitableto ablate the ROI.
 20. The method of claim 19, wherein the optical fiberand the radio frequency ablation device are enclosed within the ablationcatheter.
 21. The method of claim 20, wherein the ablation cathetercomprises a magnetic resonance imaging and radio frequency energycompatible catheter device.
 22. The method of claim 19, wherein theoptical assembly is configured to rotate the fiber optic cable toprovide a circular, forward-looking image of the ROI.
 23. The method ofclaim 19, wherein the optical assembly comprises a sheath tip, a GRINlens, a Risley prism, and a farrule, and wherein the sheath tip isstationary with respect to the fiber optic cable.
 24. The method ofclaim 1, wherein the OCT image of the ROI is acquired at 40 kHz linescan rate, 2000 lines per image, and 512 pixels per line thatcorresponds to a 6 μm and 3.1 μm pixel size in an axial and a lateraldimension respectively.
 25. The method of claim 24, wherein the OCTimage of the ROI is acquired with a full width half maximum spot size of30 μm or less over a 1 mm ROI.